Drawing the screen: BLUEBAND

       Name: BLUEBAND                                                [Show more]
       Type: Subroutine
   Category: Drawing the screen
    Summary: Clear two four-character borders along each side of the space view
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * TTX66K calls BLUEBAND
             * wantdials calls BLUEBAND


 The Elite game screen is 256 pixels wide but the Commodore 64 screen is 320
 pixels wide, which leaves 64 pixels (eight character blocks). We therefore
 show the game in the middle of the screen, and clear a four-character border
 along the left and right edges of the space view.

 This prevents graphics from spilling out of the sides of the space view (in
 particular the Trumble and explosion sprites).


.BLUEBAND

 LDX #LO(SCBASE)        ; Set (Y X) = SCBASE so it contains the address of the
 LDY #HI(SCBASE)        ; top-left corner of the four-character border along
                        ; the left edge of the screen

 JSR BLUEBANDS          ; Call BLUEBANDS to clear the left border

 LDX #LO(SCBASE+37*8)   ; Set (Y X) = SCBASE so it contains the address of
 LDY #HI(SCBASE+37*8)   ; character block 37 on the top row of the screen, which
                        ; is the top-left corner of the border along the right
                        ; edge of the screen (as there are four blocks for the
                        ; left border and 32 blocks for the space view)

                        ; Fall through into BLUEBANDS to clear the right border